Enrichment of triglyceride docosahexanoic acid by lipase used as a hydrolysis medium in lecithin-based nano-scale molecular assemblage

Docosahexanoic acid (DHA) in triglyceride from marine bioresources was successfully enriched with the aid of lipase used for hydrolysis reaction in a water in oil (W/O) microemulsion formed by soybean lecithin. Ester-bonded DHA was hardly hydrolyzed by Candida rugosa lipase, due to their steric hindrance. In contrast, mono-unsaturated fatty acid in triglyceride was easily hydrolyzed by lipase specificity, and then it was removed. W/O microemulsion formed by soybean lecithin was used as an appropriate reaction medium for hydrophobic enzyme reaction. Soybean lecithin, well-known as a biocompatible amphiphile, was employed to prepare the W/O microemulsion. Phosphate buffer (6.0 ≦ pH ≦ 7.5) was used as an aqueous phase, and 2,2,4-trimethylpentane was employed as an organic solvent. The initial reaction rate obviously depended on the water–lecithin molar ratio, which was maximum at 10. The optimal lecithin concentration was 12 mM, which was almost the same level as the critical micelle concentration in the organic solvent. Soybean lecithin was superior to AOT in obtaining a higher initial reaction rate, due to moderate electrostatic interaction. The molar fraction of DHA in triglyceride was enriched up to 97%.